The invention concerns a reactor and a process for gasifying and/or melting materials. In particular, the invention concerns the material and/or energetic utilization of any type of refuse, e.g., with principally organic constituents, but also such utilization of special waste. However, the reactor and process of the invention are also well suited for the gasification and melting of feed materials of any composition as well as for the production of energy by the use of organic substances.
Solutions to the problem of thermal disposal of various types of waste and other materials have long been sought. In addition to combustion processes, various gasification processes are known, which are aimed chiefly at achieving results with the least possible impact of hazardous substances on the environment and at reducing both the expense associated with the treatment of the feed materials and the gases that arise in the process. However, the previously known processes are characterized by an expensive technology that is difficult to manage and by the associated high disposal costs for the feed material or refuse to be treated.
DE 43 17 145 C1 describes a process based on the principle of degasification for the disposal of variously composed waste materials. In the cited process, dust-containing gases that arise are completely drawn off as circulating gas and then burned with oxygen in the melting and superheating zone. However, as tests have shown, this circulation of the gas and the likewise described exhausting of the excess gas between the circulating gas exhaust port and the likewise described exhausting of the excess gas between the circulating gas exhaust port and the melting and superheating zone do not lead to the stated goal of obtaining an excess gas that contains only very few pollutants. If the circulating gas cupola also described in the cited document is used to carry out the process, then, among other problems, the pollutant load of the excess gas is so great that the gas management this necessitates for cleaning the excess gas becomes so expensive that economical disposal of the given waste materials is no longer possible.
DE 196 40 497 C2 describes a coke-fired circulating-gas cupola for the ultilization of waste materials. This circulating-gas cupola is characterized by the fact that an additional gas vent is located below the charging hopper. The pyrolysis gases drawn off at this point are returned by a circulating-gas line to the lower section of the furnace, in which combustion of the gases occurs. Since the discharge zone for the excess gases is located above the hot zone, not only excess gases, but also a large fraction of pyrolysis gases are exhausted, so that the gas mixture also contains hydrocarbons that are difficult to remove. The subsequent gas management thus becomes extremely expensive, and the environmental load increases.
DE 198 16 864 A1, on the other hand, describes a coke-fired circulating-gas cupola, in which the excess gas exhaust system is located below the melting and superheating zone. Although the quality of the excess gases can be increased in this way, since the discharged gases are greatly reduced as they flow through the superheating zone, the spatial proximity of the superheating zone results in very hot excess gases, which must then be cooled at considerable expense. Another problem is that this configuration causes slags and dusts to start to sinter in downstream parts of the discharge-side gas line. On the other hand, the temperatures in the hearth region below the gas discharge are no longer sufficiently high to maintain the molten metals and molten slags present in this region in a molten state under various charging conditions. This interferes with or entirely prevents the tapping which must be performed.
The prior-art solutions cited above are all based on the basic principle of recirculation of a partial stream of the gases that are formed, such that the gases are drawn off in the upper region of the furnace and returned to the lower region of the furnace. The engineering world has been proceeding on the assumption that this gas circulation is also necessary for heating the feed column through use of the countercurrent principle. However, the circulating-gas principle brings the following disadvantages with it: The gases rising in the shaft furnace cool off in the feed column, so that condensation phenomena of pyrolysis products in the gas withdrawal zones, in the circulating gas lines, and in the gas jet compressors needed for returning the circulating gas lead to problems that interfere with the function of the circulating-gas furnace. During the withdrawal of the circulating gas in the prior-art processes, dust particles and small particles of refuse material are necessarily withdrawn at the same time, which, together with the condensed pyrolysis products, lead to deposits that are difficult to remove inside the entire circulating gas distribution system. Furthermore, the feed column can be heated at only a relatively slow rate by the ascending circulating gas, so that, especially in the gasification of waste materials that contain large amounts of plastics, pieces of waste material adhere to the wall of the shaft and can ultimately lead to total obstruction of the furnace.
One of the goals of the present invention is thus to develop an improved reactor and a process for gasifying and melting feed materials, which avoid the disadvantages of prior-art reactors and processes. One specific goal is to achieve simple, inexpensive, and environmentally friendly material utilization and/or energetic utilization of refuse. We would especially like to enhance the functional reliability of this type of reactor by largely avoiding the operational problems associated with the circulating-gas system. Another goal of the invention is the significant reduction of the pollutant load of the excess gas to be discharged, so that the amount of work that needs to be done in a subsequent gas purification stage can be minimized.
Pursuant to these goals, and others which will become apparent hereafter, one aspect of the present invention resides in a reactor having a charge section with a feed opening through which the feed materials are charged to the reactor from above. A pyrolysis section which has an expanded cross section is located below the charging section so that a discharge cone of the feed material can form. Gas supply devices open into the pyrolysis section substantially at a level of the expanded cross section so that hot gases can be fed to the discharge cone. A melting and superheating section is located below the pyrolysis section and has a narrowing cross section. Upper injection devices are arranged immediately below a level of the narrowing of the cross section for supplying energy-rich medium to the melting and superheating section. A reduction section is located below the melting and superheating section and has gas exhaust devices through which excess gases are exhausted. A hearth is provided with a tap below the reduction section for accumulating and draining molten metal and molten slag. Lower injection devices are provided so that energy-rich medium is supplyable directly above the molten metal and slag and below the gas exhaust devices so as to prevent solidification of the molten metal and slag. In accordance with the invention, the principle of the circulating-gas process, which has long been applied in prior-art solutions, is abandoned, and instead a shaft furnace, which operates on the countercurrent principle, is used as the reactor. By completely abandoning the conventional circulating-gas system, all of the associated problems of condensation of pyrolysis products and the formation of undesirable deposits are completely avoided. In addition, partial conglomeration of the feed materials already starts to occur in the upper part of the reactor due to the shock-like heating of the feed column, so that adherence to the inside wall of the reactor is largely eliminated. The double injection of oxygen and fuel gas (gas mixtures) allows, on the one hand, the combustion of the pyrolysis gases and, on the other hand, maintenance of a sufficiently high temperature in the lower section of the reactor, so that the molten material that collects there is kept liquid. Between the two injection devices, a reduction section is formed, through which all gases must flow before they are exhausted and in which they are therefore largely reduced.
In one embodiment of the invention, which is especially suitable for the gasification of refuse, the charging section is followed by a preliminary heat-treatment section, in which the refuse is predried, e.g., at temperatures of about 100xc2x0 C. In modifications of this embodiment, it is also possible to cool the feed materials in this section under certain circumstances in which this would be advantageous to the overall process.
One advantageous embodiment of the reactor is characterized by the fact that the total length of the charging section and the preliminary heat-treatment section is several times greater than the diameter of the charging section. This configuration causes the feed column in the charging and preliminary heat-treatment section to act as a plug that blocks the system from above and prevents excessive amounts of outside air from being drawn into the reactor.
In one modified embodiment, the upper end of the reactor is closed by a lock, a double flap valve system, or a similar device. In this way, the uncontrolled entrance of outside air and the escape of gases from the charge is avoided to an even greater extent.
It is advantageous for the reactor to have an essentially cylindrical design, and the gas feed chamber and the gas exhaust chamber have an annular design, so that the feeding and exhausting of the gas each occurs along the entire circumference of the feed column. This embodiment is suited specifically for utilization of primarily organic feed materials. Other embodiments that are more effective, for example, for other feed materials, may have noncylindrical basic shapes and devices for feeding and exhausting gases that are differently shaped and positioned.
It is especially advantageous if the pyrolysis section of the reactor is also designed with a double wall, and a heat-exchange medium is circulated in the space between the walls. On the one hand, the wall can be cooled in this way to reduce the stress on the wall material, and, on the other hand, depending on the feed material charged to the reactor and the resulting heat consumption of the feed column, additional heat can be supplied to or removed from the feed column, if necessary.
The above-stated goals of the invention are also achieved by the process for gasifying and/or melting feed materials which includes the steps of forming a feed column that is largely shielded from outside in a shaft-like reactor, shock-like heating the feed column by supplying hot gases in an upper region of the reactor to initiate pyrolysis in the feed materials, producing a hot zone at a lower level in the reactor with temperatures above 1,000xc2x0 C. by supplying energy-rich media, combusting the pyrolysis products, melting any metallic and mineral constituents that may be present, and extensive coking of residual matter of the feed materials in the hot zone, drawing all gases downward from the feed column through the hot zone and through a reduction zone located below the hot zone, drawing off reduced excess gases from the reactor in a region of the reduction zone, accumulating any molten metal and/or molten slag in a lower most section of the reactor, introducing energy-rich media directly above the accumulated molten material to maintain it in a molten state, and tapping the molten material as necessary. The process is especially suitable for the material utilization and/or energetic utilization of refuse and other feed materials.
The essential process steps of the invention can be advantageously refined by predrying the feed material by heating the feed column to about 100xc2x0 C. above the level in the reactor at which the shock-like heating occurs. This causes the water content of the feed material to be largely evaporated, which also improves the desired automatic downward movement of the feed batch. In a modified variation of the process, the feed material is not predried or may even be cooled; in the case of hot feed materials, cooling may be useful in preventing the feed material from adhering to the wall of the charging section.
It is also especially advantageous to be able to control the underpressure for exhausting the excess gases. The gases should be drawn off in such a way that, on the one hand, no gas escapes through the top of the reactor and, on the other hand, only minimal amounts of additional outside air are drawn in through the feed column. This minimization of the amount of infiltrated air present in the reactor is intended to reduce the proportion of nitrogen oxides in the excess gas and also to keep the total amount of gas low, so that the subsequent gas management can be simply designed.